Food-Entrained Feeding and Locomotor Circadian Rhythms in Rats Under Different Lighting Conditions

Jun 18, 1999Chronobiology international

How food timing and movement rhythms in rats change under different light conditions

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Abstract

Under different lighting conditions, food pulses influenced circadian rhythms in rats, with some rhythms entrained while others remained free-running.

Feeding and wheel-running activity in rats was recorded under light-dark, constant darkness, and constant light conditions.
In light-dark conditions, food pulses had minimal impact on light-entrained rhythms of feeding and locomotion.
In constant darkness, there was relative coordination between free-running rhythms and those influenced by food pulses.
Feeding activity related to food availability showed distinct phases: a peak during food access and another phase afterward.
In constant light, anticipatory activity for feeding and wheel-running was primarily linked to food pulses.
Results suggest that lighting conditions affect the establishment and maintenance of food-entrained circadian rhythms in rats.

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It has been suggested that two endogenous timekeeping systems, a light-entrainable pacemaker (LEP) and a food-entrainable pacemaker (FEP), control circadian rhythms. To understand the function and interaction between these two mechanisms better, we studied two behavioral circadian rhythmicities, feeding and locomotor activity, in rats exposed to two conflicting zeitgebers, food restriction and light-dark cycles. For this, the food approaches and wheel-running activity of rats kept under light-dark (LD) 12:12, constant darkness (DD), or constant light (LL) conditions and subjected to different scheduled feeding patterns were continuously recorded. To facilitate comparison of the results obtained under the different lighting conditions, the period of the feeding cycles was set in all three cases about 1h less than the light-entrained or free-running circadian rhythms. The results showed that, depending on the lighting conditions, some components of the feeding and wheel-running circadian rhythms could be entrained by food pulses, while others retained their free-running or light-entrained state. Under LD, food pulses had little influence on the light-entrained feeding and locomotor rhythms. Under DD, relative coordination between free-running and food-associated rhythms may appear. In both cases, the feeding activity associated with the food pulses could be divided into a prominent phase-dependent peak of activity within the period of food availability and another afterward. Wheel-running activity mainly followed the food pulses. Under LL conditions, the food-entrained activity consisted mainly of feeding and wheel-running anticipatory activity. The results provide new evidence that lighting conditions influence the establishment and persistence of food-entrained circadian rhythms in rats. The existence of two coupled pacemakers, LEP and FEP, or a multioscillatory LEP may both explain our experimental results.

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Food-Entrained Feeding and Locomotor Circadian Rhythms in Rats Under Different Lighting Conditions

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